Autism spectrum disorder (ASD) is a continuum of neurodevelopmental characteristics that includes deficits in communication and social interaction, as well as restrictive, repetitive interests and behaviors. ASD is an increasing public health concern, with about 1 in 45 American children diagnosed with ASD in 2014, a 10-fold increase in prevalence over the past 40 years. The effect of ASD on both society and the economy is a large burden, estimated at more than $286 billion per year in the U.S. alone. While a single direct link to ASD diagnosis has not been determined, studies have identified genetic, epigenetic, neurological, hormonal, and environmental factors that affect outcomes for patients with ASD. In order to effectively treat patients with ASD, timely detection is crucial for implementation of early treatment options. Using knowledge of these preexisting factors for ASD, doctors can begin treatment while the patient is still young, even if the child has not begun to exhibit typical ASD symptoms. Studies suggest that earlier treatment results in better functional outcomes and reductions in symptoms of ASD. These models, medications and programs have proven to be effective in managing the symptoms of ASD, and may remove some patients from the ASD spectrum entirely. Unfortunately, current diagnostic methods for ASD are not very accurate for young children; the average age of diagnosing ASD is three years old, and about half of those are false positives. Development of accurate diagnostic biomarkers for ASD would thus represent a valuable addition to patient care. Quadrant Biosciences is developing an approach to diagnose ASD by measuring brain-related and other ribonucleic acids (micro, circular, and bacterial) in saliva. Extracellular transport of miRNA via exosomes and other microvesicles is an established epigenetic mechanism for cells to alter gene expression in nearby cells. This has enabled Quadrant to measure genetic material that may have originated from the central nervous system simply by collecting saliva. This method minimizes many of the limitations associated with analysis of post-mortem brain tissue (e.g., anoxic brain injury, RNA degradation, post-mortem interval, agonal state), or peripheral leukocytes (relevance of expression changes, painful blood draws) employed in previous studies. Alterations in the human microbiome (i.e., microbial communities) have also been shown to correlate with ASD. Thus, extracellular RNA quantification in saliva provides an attractive and minimally invasive technique for biomarker identification in children with ASD. This Phase II study will test the hypothesis that a pre-defined panel of human and non- human RNAs will accurately determine ASD status in a cohort of 1600 children ages 18 months to 6 years. Using prospective clinical trial methodology, with input from FDA, the project will provide data essential to the commercialization of Quadrant?s ASD diagnostic technology, further testing the algorithm with the inclusion of additional children and following children who are flagged with the currently utilized ASD to determine their ultimate diagnosis.